This invention generally relates to catheters, and particularly protective sheaths for intravascular catheters for such as balloon catheters used in percutaneous transluminal coronary angioplasty (PTCA) or for the delivery of stents.
In percutaneous transluminal coronary angioplasty (PTCA) procedures a guiding catheter is advanced in the patient's vasculature until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire is first advanced out of the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guidewire crosses a lesion to be dilated. A dilatation catheter, having an inflatable balloon on the distal portion thereof, is advanced into the patient's coronary anatomy over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with inflation fluid one or more times to a predetermined size at relatively high pressures so that the stenosis is compressed against the arterial wall and the wall expanded to open up the vascular passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter and the guidewire can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate of angioplasty alone and to strengthen the dilated area, physicians now normally implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel or to maintain its patency. A tubular cover formed of synthetic or natural material may be present on an outer or inner surface of the stent. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded within the patient's artery to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. See for example, U.S. Pat. No. 5,507,768 (Lau et al.) and U.S. Pat. No. 5,458,615 (Klemm et al.), which are incorporated herein by reference.
It is conventional practice to fold the deflated balloon about the tubular inner member of the catheter and then advance a protective sheath with an inner diameter larger than the outer diameter of the folded balloon over the folded balloon to hold the balloon in the folded condition for subsequent packaging and sterilization. In addition to protecting the balloon in storage and transit, the sheath holds the folded balloon in position so that, when sterilized at elevated temperatures, the balloon is heat set in the folded condition. A folded balloon presents a much smaller profile than an unfolded balloon and thus is more easily advanced through a patient's vascular system. Moreover, being heat set in the folded condition, the balloon returns in part to the folded condition when subjected to a vacuum after being inflated, such as when venting air from the interior of the balloon and catheter. To facilitate advancing the protective sheath over a folded balloon the sheath is frequently formed of a lubricous fluoropolymer material. Unfortunately, the fluoropolymer protective sheath is usually quite hard and it does not conform to the shape of the folded balloon, so care must be exercised in advancing the sheath over the folded balloon on the catheter and in subsequent handling so that the balloon is not damaged by the protective sheath.
Protective sheaths are described in numerous U.S. Patents, for example, U.S. Pat. No. 5,425,710 (Khair et al.), U.S. Pat. No. 5,033,007 (Euteneuer), U.S. Pat. No. 4,710,181 (Fuqua), U.S. Pat. No. 4,738,666 (Fuqua), U.S. Pat. No. 4,540,404 (Wolvek), U.S. Pat. No. 5,066,298 (Hess), U.S. Pat. No. 5,116,318 (Hillstead) and U.S. Pat. No. 5,417,707 (Parkola). All of the above references are incorporated herein by reference.
While there has been much development effort in protective sheaths for balloons and catheters, none of the sheaths heretofore developed have been completely satisfactory. These prior sheaths have been either very difficult to slide over or otherwise apply to a folded balloon, or they have been difficult to remove from the balloon before the catheter is inserted into the patient. The present invention provides a protective sheath which eliminates or minimizes the problems of these prior sheaths.